Wobble

BadDog,

if my info is correct, a .057gasket and all else the same would yield about 9.8-1.

at this point going to go for the extra 3cc in the chamber + cut the pistons to get as close to, or below 9.5-1 as possible.

Actualy the engine guy just called, they have just got done cutting one piston using the specs RMbuilder supplied.

He cc'd it in the hole and came up with 9.38-1. This is what we will go with. Not 9-1 but it saves the pistons and should be ok for 92 octane.

I would love to re-coat the pistons, however Polydyn is running 2-3 weeks turnaround at the moment and I have been boatless since Good Friday already.

Thanks for everyones help I'll try and get a picture of the cut pistons in the morning.

cstraub

Get a hold of Techline Coatings. You can do it yourself for about 40 bucks. All that is required is a covential oven.

Chris

Wobble

Thanks for the info Chris, I am checking into it http://www.techlinecoatings.com/Engine.htm As you can see from the above picture the pistons are coated top and sides with Polydyn. The only area not coated will be where we remove material from the dome.

Wobble

Piston cut to safe min thickness with edges of cut chamferred.

Should have engine back today. Was going to thrash all day tommorrow and get it installed, but wife says kids don't recognize me anymore so I'd better spend some quality time

Raylar

You might want to be careful with the ceramic top coat on the pistons with iron heads. Its been our expierence that the coating can raise the cylinder temperature in a big block iron head motor much higher than it will be in an aluminum head bbc motor. Your piston detonation point and damage is in the quench area not in the combustion chamber indicating you had possible pre-ignition in that area. You could be having a detonation issue with 34 to 36 degree timing and high cylinder temperatures with todays rot gut fuel. I would suggest not using the ceramic top coat in this motor. Just my opinion.

Ray @ Raylar

Steet

I took the stock J & E pistons out of my crate 502 and had them cut to flat tops for a blower motor. J & E told my mechanic how much he could take off safetly. There was just a slight valve relief left after cutting. I lowered my CR from 8:75 to 8:00 and I ran merlin cast iron heads with 8 lbs of boost with 32 degrees of timing and never had a detonation problem or a problem with the pistons.
Just have to be careful with poor gas

Wobble

Bob,

You were spot on, I found the air leak, talk about a 10 cent part.

Apparently when starting the motor that morning I had a slight backfire which pushed the cap off the vacuum port that goes to the butterfly closest to #2 cylinder.

With the engine already on the edge because of the high compression that was the final straw.

I have now tie-wraped all vacuum port caps on the carb.

Took the boat out last night and ran 72mph on glass smooth river water at 80* air temp, which is as good as it ran before in those conditions.

Again, thanks to everyone for their input on this thread.

rmbuilder

Mark,
Glad you found the lean condition, otherwise the engine would have failed again. All the signs pointed away from detonation, gas quality, and timing. The (1) piston crown being uncolored, the whole being in the quench area, the fault area being melted not shattered, and the other 7 showing no signs of failure. The SRP’s have less elasticity than the JE’s and when the crown lost integrity the land area shattered. Considering the C/R of the engine the other pistons looked quite good. Don’t know if any valid observations can be made from the other seven regarding the effectiveness of the thermal barrier coatings or not.
Bob